[Pynctyncroast]

Pre-paid card can be bought in corner shops like 7-Eleven. The following information comes from the Lonely Planet message board:

Quote[/b] ]Mobiles and sims can be purchased in the MBK Center. The best pre-pay scheme is One2Call. It's the only sim on pre-pay that will let you call internationally. All phones can be unlocked at the MBK Center too, so if you already have a mobile that is barred from using other providers, it can be done there, regardless of make and model. One2call sim costs 550 baht and 500 baht calling credit is included. Phone unlocking costs about 300 baht.

One more thing. Using the One2Call network is cheaper than using Lenso (and other) phone boxes on the street for international calls!